The present invention relates to friction drive and sheet advancing means which includes plural friction rolls and is used in printers.
Printers are, for example, constructed in that a friction roll advances a sheet or the current end portion of a roll of paper or other web material onto a platen, and a print head is moved across to print a line. Thereafter, the paper is advanced by whatever distance is deemed appropriate for printing the next line. In some cases, a single print head serves and services two different sheets which are advanced independently by individual friction rolls. Individual sheets are cut from each roll, such as individual tickets.
The friction rolls of these known printers are axially aligned therein. One roll is usually being driven from one side and the other roll is driven from the other side. Printers of the type with several friction driven rolls, but also those with an individual friction roll, often operate with paper having certain information already printed on, and the printer merely supplements the printed content and information. A friction drive here has the disadvantage that a certain amount of slip is inevitable so that the newly printed matter may not be very accurately registered with the preprinted information. Thus, one needs to make certain adjustments to compensate such slippage which may be cumulative, otherwise such adjustment may be aided by markings which are scanned.